1. Field of the Invention
This invention relates to a screen fixing structure, and more particularly relates to a transparent screen fixing structure to be applied to a four-surface multi-projection display that projects light onto the back surface of a liquid crystal screen.
2. Description of the Prior Art
FIG. 6 is an exploded perspective view showing a conventional screen fixing structure for a projection display. In the figure, reference numeral 1 denotes a screen called a thick type screen. The screen 1 is composed of a lenticular lens 1a made of an acrylic resin and having a thickness of about three millimeters and a Fresnel lens 1b made of an acrylic resin and having a thickness of about three millimeters; the tops of both the lenses 1a and 1b are affixed to each other with a pressure sensitive adhesive double coated tape 9.
Reference numeral 7 denotes holders; the cross sections of them are formed like a crank; one side edges of the holders 7 are hung on the fringes of the screen 1, and the other side edges of them are fixed to acceptance seats formed on the fringes of a frame 8 by means of screws 6 for holding the screen 1. The holders 7 are disposed on four sides of the screen 1; the screen 1 is fixed to the frame 8 by being strongly pressed by the holders 7 disposed on the upper side of the screen 1. The holders 7 disposed on the other sides of the screen 1 fix the screen 1 to the frame 8 loosely in such a degree that the screen 1 does not move much between the frame 8 and the holders 7 owing to the influence of external force or the like.
The frame 8 and the holders 7 are generally made of metal or plastic.
Next, the operation thereof will be described.
When the screen 1 expands due to the change of temperature and humidity in the state of the screen 1 fixed as described above, the force that extends the screen 1 to the right and the left directions and the down direction where the screen 1 can move works on the screen 1 greatly owing to the rigidity of the screen 1, so that the screen 1 slips to move by the amount of the expansion thereof between the frame 8 and the holders 7.
The constriction of the screen 1 owing to the change of temperature and humidity also makes the screen 1 slide to move into the direction opposite to the direction at the time of the expansion thereof by the amount of the constriction between the frame 8 and the holders 7.
The above-mentioned structure prevents the large warp and the large deformation of the screen 1 by disposing the holders 7 at appropriate positions on the frame 8 for holding the screen 1 with the pressing force having the strength in the degree capable of allowing the extension and the constriction of the screen 1.
Furthermore, FIG. 7 is a partial perspective view showing a main part of another conventional screen fixing structure disclosed in, for example, Japanese Unexamined Publication of a Utility Model No. 171470/84 (Jikkai-Sho No. 59-171470). FIG. 8 is a back view of the screen fixing structure shown in FIG. 7. In these figures, reference numeral 1 denotes a screen composed of the lenticular lens 1a and the Fresnel lens 1b opposed to the lenticular lens 1a. Reference numeral 16 denotes a frame for fixing the screen 1 on it. Reference numeral 20 denotes the cuts of the shape of letter U and formed at the central parts of the four sides of the screen 1 respectively so as to penetrate the parts of the screen 1.
Reference numeral 24 denotes checks inserted into the cuts 20 and fixed on the frame 16; the checks 24 have heads 26 whose diameters are larger than the widths of the cuts 20.
The screen 1 is disposed to be fixed between the heads 26 and the frame 16. The lenticular lens 1a and the Fresnel lens 1b are pressed to each other to be fixed in a degree capable of moving in the direction of the cuts 20 mutually.
Next, the operation thereof will be described.
As shown in FIG. 8, when the screen 1 expanded (to the degree shown by the broken line) from the ordinary fitted state (shown in the solid line) thereof owing to the change of temperature and humidity, the lenticular lens 1a and the Fresnel lens 1b mutually move to the direction of the cuts 20 for preventing the large distortion of the screen 1 itself.
The conventional screen fixing structures are formed as described above. If the conventional structures are applied to a four-face multi-projection display using, for example, liquid crystal displays as light bulbs, the amount of the warp of the screen, which warp causes the distortion of a picture, must be as small as possible, and the joint parts of the screen must not move even when the screen expands or contracts, because the distortion of a picture cannot eclectically be corrected owing to the structure of the screen. But, the conventional screen fixing structures cannot satisfy the above-mentioned conditions. Consequently, the conventional screen fixing structures have the defect that good pictures cannot be obtained because pictures projected from a plurality of projectors cannot constitute a complete picture owing to the warp of the screen and the movements of the joint parts thereof.
The conventional screen fixing structures have not the particular reinforcing means for a screen which means can effectively prevent the generation of a warp and be easily fabricated and adjusted. Consequently, the conventional structures have the defect that good pictures cannot be obtained because the warps, which have been generated owing to the expansion or the constriction of the screen caused by the changes of temperature and the like after the fabrication of the screen, have been accumulated to produce a great warp over the whole large screen.
Furthermore, the conventional screen fixing structure has also the defect that its reliability decreases because the warp and the distortion of the screen becomes easy to generate under the circumstances where the screen is apt to receive vibrations and impulses owing to the lack of the reinforcing means.